Hi,
I got a South African ball python in Nov 2014. She is 1 ½ yrs. old.I too had problems keeping my humiditylevel to 70 and up.What I did was. I took bathroom hand towel and covered it with foil then put duct tape around the entire outside frame. Then I put a wet (wring out access water) under the foil towel and cover entire tank with a bath towel (minus area with heating light) I put 4 little stripes of foil around heating light. So now, the entire top of the tank is covered. I guarantee if you do this, your humidity level will stay at 70 and up all day. I wet the towel once daily before I go to bed and the humidity stays to 70 or higher. If you find the humidity, levels going under 70 repeat the wetting of the towel.
Brenda